Yokota T, Milenic D E, Whitlow M, Schlom J
Laboratory of Tumor Immunology and Biology, National Cancer Institute, NIH, Bethesda, Maryland 20892.
Cancer Res. 1992 Jun 15;52(12):3402-8.
Single-chain antigen-binding proteins, or sFvs, represent potentially unique molecules for targeted delivery of drugs, toxins, or radionuclides to a tumor site. In previous studies (Cancer Res., 51:6363-6371, 1991) using a human colon carcinoma xenograft model, it was demonstrated that the sFv has an extremely rapid plasma and whole body clearance, as compared to intact IgG or Ig fragments. One potential consequence of the rapid sFv pharmacokinetic properties was the reduced percentage of injected dose/g of the radiolabeled sFv found in the tumor throughout a range of time points. The present study was designed to define the tumor penetration properties of a radiolabeled sFv in comparison with other Ig forms. 125I-labeled sFv, Fab', F(ab')2, and IgG forms of monoclonal antibody CC49, directed against the human pancarcinoma antigen TAG-72, were used to target the LS-174T human colon carcinoma xenograft in athymic mice. At various time points after systemic Ig administration, quantitative autoradiographic analyses of surgically removed tumors were used to define the rate and degree of penetration of the various Ig forms. These studies revealed that most of the intact IgG delivered to the tumor was concentrated in the region of or immediately adjacent to vessels, while the sFv was more evenly distributed throughout the tumor mass. The distributions of the Fab' and F(ab')2 fragments showed intermediate penetration in a size-related manner. The sFv demonstrated maximum tumor penetration at 0.5 h postinjection, while the intact IgG reached an equivalent degree of penetration at 48 to 96 h postinjection. These studies thus reveal a greater degree of uptake throughout the tumor for the sFv than would be expected by gross analyses of percentage injected dose/g and demonstrate an extremely rapid tumor penetration of the sFv. These studies should aid in the rational design of potential applications of drug-, toxin-, and radionuclide-conjugated sFvs in cancer therapy.
单链抗原结合蛋白，即单链抗体片段（sFv），是一类极具潜力的独特分子，可用于将药物、毒素或放射性核素靶向递送至肿瘤部位。在先前的研究（《癌症研究》，51:6363 - 6371，1991）中，使用人结肠癌异种移植模型表明，与完整的IgG或Ig片段相比，sFv在血浆和全身的清除速度极快。sFv快速的药代动力学特性的一个潜在后果是，在一系列时间点内，肿瘤中放射性标记的sFv每克注射剂量的百分比降低。本研究旨在确定放射性标记的sFv与其他Ig形式相比的肿瘤穿透特性。针对人胰腺癌抗原TAG - 72的单克隆抗体CC49的125I标记的sFv、Fab'、F(ab')2和IgG形式，被用于靶向无胸腺小鼠体内的LS - 174T人结肠癌异种移植瘤。在全身给予Ig后的不同时间点，对手术切除的肿瘤进行定量放射自显影分析，以确定各种Ig形式的穿透速率和程度。这些研究表明，递送至肿瘤的大多数完整IgG集中在血管区域或紧邻血管的区域，而sFv在整个肿瘤块中分布更为均匀。Fab'和F(ab')2片段的分布呈现出与大小相关的中间穿透情况。sFv在注射后0.5小时显示出最大的肿瘤穿透，而完整IgG在注射后48至96小时达到同等程度的穿透。因此，这些研究揭示了sFv在整个肿瘤中的摄取程度比通过每克注射剂量百分比的粗略分析所预期的要高，并证明了sFv极快的肿瘤穿透性。这些研究应有助于合理设计药物、毒素和放射性核素偶联的sFv在癌症治疗中的潜在应用。
